Three isolates of the entomopathogen Beauveria bassiana along with one strain of Metarhizium anisopliae were cultured on seven media with different ca

Insects face diverse biotic and abiotic stresses that can affect their survival. Many of these stressors impact cellular metabolism, often resulting in increased accumulation of reactive oxygen species (ROS). Consequently, insects will respond to these stressors by increasing antioxidant activity and increased production of heat shock proteins (HSPs). In this study, the effect of heat, cold, starvation, and parasitism by Habroacon hebetor wasps was examined in the carob moth, Ectomyelois ceratoniae, to determine which responses were common to different stresses. For all stressors, malondialdehyde levels increased, indicative of oxidative stress in the insects. The activity of two antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT), increased with each stress, suggesting that these enzymes were serving a protective role for the insects. Heat (46°C for 100 min) and cold (-15°C for 30 min) treatments caused significant mortalities to all developmental stages, but pretreatments of moderate heat (37°C for 10 min) or cold (10°C for 10 min) induced thermotolerance and reduced the mortality rates when insects were subsequently exposed to lethal temperatures. Quantitative RT-PCR confirmed that heat and cold tolerance were associated with up-regulation of two HSPs, HSP70 and HSP90. Interestingly, HSP70 transcripts increased to a greater extent with cold treatment, while HSP90 transcripts increased more in response to high temperatures. RNA interference (RNAi)-mediated knockdown of either HSP70 or HSP90 transcripts was achieved by injecting larvae with dsRNA targeting each gene’s transcripts, and resulted in a loss of acquired thermotolerance in insects subjected to the heat or cold pretreatments. These observations provide convincing evidence that both HSP70 and HSP90 are important mediators of the acquired thermotolerance. Starvation and parasitism by wasps caused differential expression of the HSP genes. In response to starvation, HSP90 transcripts increased to a greater extent than HSP70, while in contrast, HSP70 transcripts increased to a greater extent than those of HSP90 during the first 48 h of wasp parasitism. These results showed the differential induction of the two HSPs’ transcripts with variable stresses. As well as, heat, cold, starvation, and parasitism induce oxidative stress, and antioxidant enzymes likely play an important role in reducing oxidative damage in E. ceratoniae.

Plant extracts are currently studied more and more because of the possibility of their usage in plant protection. Many of the natural plant compounds which are used in the control of pests are known to affect the digestion and immune functions of insects. In this study, effects ofArtemisia annuaextract on the digestive enzymatic profiles and the cellular immune reactions ofEurygaster integricepswere investigated to reach a better understanding of its role in the control of this pest as the most destructive one in the production of wheat in the Near and Middle East, eastern and southern Europe and North Africa. Feeding and injection methods were used to study the plant extract effects on digestive enzymes and cellular immunity, respectively. When adultE. integricepsfed on food and water containing plant extracts, activity of the digestive enzymes, including α-amylase, α- and β-glucosidases, protease and lipase, in addition to cellular immune reactions (total and differentiate hemocyte numbers, phagocytosis, nodule formation and phenoloxidase activity) againstBeauveria bassianawere affected and significantly decreased in comparison with controls, in that the clear dose-response relationships were established with respect to enzyme activities and immune reactions.A. annuaextract had a significant effect on kinetic parameters (V_maxandK_m) of digestive enzymes and phenoloxidase activity so that the presence of the plant extract decreased the value ofV_maxand increasedK_m, causing the reduction of enzyme affinity to the substrate, overall velocity of the reaction and finally interfering with the rate of breakdown of the enzyme-substrate complex. The understanding of fungal-induced immune responses and identification of factors regarding fungal virulence could be important in accelerating host death in a biological control scenario. Hence, the combination of botanical pesticides and microbes to control insect pest populations would be a safe and possibly rapid method to decrease their damage and environmental risk due to the use of chemical pesticides.

The effects of Beauveria bassiana spores and its secondary metabolite on insect resistance to an organophosphorus insecticide, fenitrothione and secondary metabolite effects on acetylcholine esterase inhibition were investigated. Findings showed that fungal spores and its secondary metabolite increase total esterase and glutathione S-transferase activities in the hemolymph of infected and treated adults of Eurygaster integriceps. But the fungal secondary metabolite had an adverse effect on AChE activity of adults that decreased its activity level and isoforms of this enzyme in polyacrylamide gel electrophoresis. Fungal infection decreased the susceptibility of E. integriceps adults to fenitrothione, in comparison with uninfected individuals. Possible involvement of detoxifying enzymes in the development of insect resistance to fenitrothione should be considered in combined usage of chemicals and microbial agents for integrated pest management programs.